A simple but useful change of the conventional mathematical formalism leading to compartmental models used in representing physiological kinetics is the designation of some of the system flows as controlled flows. The magnitude of such flows is considered as controlled in time by some designated variable in the system. Controlled flows may then be used in representation of physiological systems in a way analogous to controlled current and voltages sources in electrical networks. Such models will be useful in representing system response to disturbances in the system and in exploring the changes in system structure related to diseased states. This project will explore the control structure of such systems with particular emphasis on controllability and identifiability. Controllability yields a criterion on which the appropriateness of a model may be judged while identifiability determines the appropriateness of experimental design in investigating systems. Specific cases will be sought where diseased states can be related to changes in controlled flows.